Light Leak

<p>Help! I recently bought a A12 with the "flying V" on the release button along with a 500C. I ad had light leak problems with an earlier back which I had to replace the seal on (successfully) so I did a preemptive seal replacement on my recently purchased back. After running a roll of Ektar 100 through it there were leaks on about 3/4 of the photo. I tried to reinstall the seal figuring I had not seated it properly but the next roll of Portra 800 was even worse. I notice the spaces between he images varies a little - on actually overlap but come darn close ant the edges of the image don't form a nice crisp edge. I'm assuming I'm looking at a repair to cure the spacing but does anyone have any ideas about the leak. Do leaks happen other than through the dark slide slot. The back itself looks to be in very good shape and serial numbers match.</p><div></div>

<p>Where was the sun/main light source with reference to the camera back? Inspect the darkslide slot, its a likely suspect.</p>

<p>Modern film base is thinner than it was in years past. Roll film holders made in the 1970's or earlier will have errors due to film base thickness, holders made in the 1980's or later might have film base errors.<br>

Two systems were used in roll film holders, a clutch system that responds to load based on frame number and mechanical geared. In the clutch system the tension required to move the film a given amount is sensed and when that limit is reached the film quits moving even if the lever is not at its mechanical limit. Wear can result in the clutch slipping prematurely resulting in film not being moved far enough causing overlapping of frames. Cleaning and adjusting the drive system is necessary to correct problems.<br>

In a mechanical geared system the film is advanced a fixed amount with a cam machined for the frames based on the film thickness. To correct frame spacing in this type of system the take up spool inter diameter must be increased or the diameter of the roller on the take up side increased by .012 to .016 inch depending on the vintage of the roll film holder. This results in the same amount of film per frame to be moved further.<br>

Current film backing paper is .006 inch. Kodak and Ilford films are on a .0045 inch thick base, Fuji is on a .0035 inch thick base. Older films were on a .005 or .006 inch thick base.<br>

The uneven edge is caused by the film not being flat in the film plane. This can be caused by the advance system or the supply side tension spring being weak.</p>

Here is a theory: the space between frames doesn't have a light leak, so maybe it isn't the mag seal. Could it be the baffle

in the camera not closing all the way?

<p>Good thinking Michael, the light leak is primarily within the frame area therefore it is in front of the gate. This sort of deduction is required for tracing a light leak and the shape and intensity of the flare are also clues. In the images that are shown here I can say with total confidence that the slide aperture is the place that the light is getting in, if it was the body shutter there would be more horizontal features to the flare. The spacing is close, I would recommend a service (CLA).</p>

<p>Just put black tape over the dark slide slot next roll, see if the light leak stops.<br />I still bet its the dark slide seals that are leaking......just try this.<br />And yes it will show up faster with higher speed film.</p>